This invention relates to electrolytes for electrolytic devices and has specific pertinence to an improved low temperature electrolyte which provides a high sparking voltage for use in capacitors.
Those skilled in the art are aware that virtually every dielectric oxide film electrolytic capacitor formed by conventional electroforming techniques are possessed of numerous imperfections and irregularities which increase the leakage current and reduce the dielectric strength in capacitors. The addition of an electrolyte serves not only as a conductive solution for transporting electrical charges between the anode and the cathode, but also provides oxygen for repair of the imperfect anodic dielectric film.
Among the many desirable characteristics of a capacitor electrolyte, perhaps the most difficult to achieve is a high sparking voltage over a broad range of operating temperatures. This problem is most acute in the low temperature range, for example, between -40.degree. C. and .dbd.55.degree. C. A high sparking voltage indicates an ability of the electrolyte to resist chemical breakdown at high voltages. Such breakdown causes arcing between the capacitor electrodes which, in most instances, causes catastrophic failure of the capacitor.
Prior to the present invention, high voltage electrolytes (350 to 500 volts) have been composed of boric acid, ammonia and/or ammonium pentaborate dissolved in ethylene glycol. The highest sparking voltage obtainable with this sytem is about 525 volts, and its low temperature characteristics are poor because of the viscous nature of the system. The electrolyte of the present invention provides a sparking voltage of at least 620 volts.